Point Source Microscope

The PSM is an unusually flexible optical test instrument with many unique features that set it  apart from other optical test instruments. This is why we call it the “Swiss Army Knife” of  optical instruments.

As opposed to most optical test instruments, the PSM is lightweight and has a small physical footprint. This means the PSM is used and mounted in places many other instruments cannot be  used because of their size and mass. The PSM is easily mounted on a common xyz stage found in most optical labs and shops, and is easily built into other optical test instrumentation. 

The PSM is multiple instruments in one like the Swiss Army Knife; used with a microscope objective it is an autostigmatic microscope useful for measuring radii of curvature and optical  alignment among other uses, while used without an objective it is an autocollimator with a small  aperture that is particularly useful for measuring errors in small prisms and windows.

The PSM is sensitive to a very wide range of intensities due to an adjustable internal laser diode  light source and an adjustable camera. The internal source has a bright mode for aligning the  PSM under ambient lighting of about 0.3mW and an adjustable range to avoid camera saturation  of 25 μW down to 25 pW. The camera shutter is controllable over a range of 1000 and has a gain  of 10. This gives a total dynamic range of intensities of easily handled of about 10⁸.  

While on the subject of intensity, the PSM is a Class I laser device so it may be used without laser safety restrictions as long as the PSM case remains closed. If additional power is needed the PSM may be coupled to an external light source via a single mode fiber. In addition, this feature  gives the flexibility to use the PSM at any desired wavelength from 350 nm to over 2 μm.  Clearly the PSM is not optimized over this wavelength range but it can still be used productively  over this range (and with the appropriate camera for use beyond 1 μm). 

In addition to being an autostigmatic microscope, the PSM is also a full field video microscope that is parfocal with the autostigmatic focus so you can see where the reflected spot focus is coming from. This is useful in case the reflected spot appears asymmetrical where it should not.  The microscope may be focused on contamination or a defect in the surface being examined. 

The sensitivity to focused spot motion is adjustable by changing objectives. While the PSM is supplied with a 10x objective, it will work with any infinity corrected objective from 100x to 2x.  For even lower magnification and wider field of view, a simple plano-convex lens with an efl up to 150 mm may be used with the expected loss of lateral sensitivity. 

Finally, just like a Swiss Army Knife, the PSM is completely portable. It has two USB cables to a laptop computer that is supplied with the PSM and is powered by the laptop which has the  PSM Align software installed. The PSM is ready to use when received. Plug in the two USB cables, boot the computer, click on the PSM icon (be a little patient), and the video screen  appears. You are now ready to work.

The Point Source Microscope makes optical system alignment easy and deterministic, letting you perfectly align each component’s center-of-curvature and on-axis focused beam to the exact specifications. With both bright field imaging and autostigmatic microscopy, the PSM lets you align all optically important features quickly. Ergonomic features such as a bright laser diode setting make alignment simple, even in full room light. 

The PSM lets you align the actual optical features, rather than relying on mechanical datums, so you can relax mechanical tolerances on your optics and mounts to reduce system costs. Use the PSM for everything from simple optics to complex systems such as Offner relays, atmospheric error correction systems and off-axis telescopes.

The PSM is invaluable for aligning aspheric optics, including off-axis aspheres. The PSM locates point images and shows the image shape as a star test.  This unique system reduces alignment error to near zero by keeping the image in the correct location while adjusting the asphere to minimize aberrations.

The PSM serves as an excellent incoming quality inspection tool, enabling fast verification of image shape, with λ/8 sensitivity, so you can easily resolve out-of specification optics without the expense or complication of using an interferometer. Further, the PSM can measure radius of curvature for production control, verify whether a lens meets specifications, or verify that a lens is correctly oriented. The PSM can even be mounted on a CMM for precise, non-contact x-y-z location.

We are often asked if the PSM can be used at wavelengths other than the standard internal laser diode and LED sources at 635 nm. The answer is definitely yes by coupling in an external fiber feed light source.

The PSM performs to original specifications all the way from 405 to 1080 nm without any modification.

This makes the PSM useful for aligning laser diode sources to other components in an optical system, for example. The useful spectral range for the PSM may be even greater, we simply have not tried over an even broader range.